[Sensitivity of bovine and equine streptococci to beta-lactam antibiotics (benzylpenicillin, ampicillin, oxacillin, cefotaxime) in the agar diffusion and E-test].

This research article investigates the sensitivity of certain strains of streptococci found in cows and horses to four beta-lactam antibiotics. Testing methods were applied in various agricultural regions in Germany. The results indicate that the majority of the isolates were sensitive to the tested antibiotics.

Research Context and Objectives

• The research focuses on a total of 559 streptococcal strains which were 368 from udder secretions of cows (Sc. agalactiae, Sc. dysgalactiae, Sc. uberis) and 191 from horse specimens (Sc. equi ssp. zooepidemicus, Sc. equi ssp. equi).
• The specimens were gathered from various agricultural regions in Germany such as Lower Saxony, in particular the region of Weser-Ems, Bavaria, and Altmark.
• The main objective of the study was to investigate the sensitivity of these strains to four beta-lactam antibiotics namely: benzylpenicillin, ampicillin, oxacillin, cefotaxime.

Methods of Testing

• Two different test methods were applied to determine the sensitivity of the strains to the antibiotics: the agar diffusion test for determining the diameter of the zone of inhibition and the E-test for determining the minimal inhibitory concentration (MIC).

Results and Findings

• As per the evaluation code of DIN 58,940, an overwhelming majority, 98% to 100% of the isolates from the cow udder as well as of the Streptococcus strains from horses, were found sensitive to all four antibiotics tested.
• The only exception was Sc. uberis, which showed slightly lesser sensitivity to benzylpenicillin (79.7%) and Oxacillin (83.2%).
• No significant difference was observed in the sensitivity to beta-lactams among strains from different agricultural regions.
• When compared to the MIC reference values, the agar diffusion test results exhibited only a minor error rate of between 1.62% (for ampicillin) and 5.21% (for benzylpenicillin), demonstrating a satisfactory agreement between the two testing methods.